Modern telecommunications networks generally include two separate communication pathways or subnetworks. The first is a voice network that handles the transmission of voice or other information between users. The second is a signaling network that facilitates the dynamic linking of a plurality of voice network circuits, such that a voice-type connection is established between a calling party and a called party. These functions are generically referred to as call setup and call tear down. Additionally, the signaling network provides a framework through which non-voice related information can be transported in a manner that is transparent to the user. This signaling technique is often referred to as “out of band” signaling, where the term “band” implies voice band. Common examples of such out of band data transport are the access of 800 number database services, calling card verification services, number portability services, and caller ID services.
In order to provide consistent and reliable communication across the signaling network infrastructure, a common or standard digital signaling protocol known as SS7 has been developed. SS7 is an out of band common channel signaling system that uses labeled messages to transport circuit related signaling information, non-circuit related signaling information, network resident database service information and other information that can be used for the establishment of communication services.
From a hardware perspective, an SS7 network includes a plurality of SS7 nodes, generically referred to as signaling points (SPs), that are interconnected using signaling links, also referred to as SS7 links. At least three types of SPs are provided in an SS7 network: service switching points (SSPs), signal transfer points (STPs), and service control points (SCPs).
An SSP is normally installed in tandem or Class 5 offices. The SSP is capable of handling both in-band signaling and SS7 signaling. An SSP can be a customer switch, an end-office, an access tandem and/or a tandem. An STP transfers signaling messages from one signaling link to another. STPs are packet switches and are generally installed in mated pairs. Finally, SCPs control access to databases, such as 800 number translation databases, 800 number carrier identification databases, credit card verification databases, etc.
Signaling datalinks are transmission facilities used to connect SPs together. They are dedicated bidirectional facilities operating at 56 kbps in the U.S. and Canada and at 64 kbps when clear channel capability is deployed. Normally, every link has a mate for redundancy and enhanced network integrity.
Signaling datalinks include access links or “A” links that connect SSPs to STPs and that connect SCPs to STPs, as shown in FIG. 1. Bridge links or “B” links are used to connect mated STPs to other mated STPs that are at the same hierarchical level, as shown in FIG. 2. Cross links or “C” links connect mated STPs together, as shown in FIG. 3. C links are used for passing messages between STPs when signaling network failures are encountered.
Diagonal links or “D” links connect STPs of different hierarchical levels, as shown in FIG. 4. Extended links or “E”, links connect SSPs to STPs that are not within their associated local STP area, as shown in FIG. 5. Finally, fully associated links or “F” links connect SSPs directly together without STPs, as shown in FIG. 6. FIG. 7 is a block diagram of a two-level SS7 network including a summary of possible link deployment.
SS7 also includes a network protocol. As a protocol, SS7 defines a hierarchy or structure of the information contained in a message or data packet that is transmitted between SPs of an SS7 network over signaling links. This internal data structure is often referred to as an SS7 protocol stack which includes the following four SS7 levels:                Level 1: The Physical Level        Level 2: The Datalink (or Link) Level        Level 3: The Network Level        Level 4: User Parts and Application Parts Level        
The physical level, also referred to as message transfer part (MTP) level 1, is the lowest or most fundamental level and is the first level that is used to interpret and process an incoming message. This level determines and/or provides the electrical characteristics to transmit the digital data over the interface being used. Following interpretation/processing at the physical level, the incoming message is passed up the stack to the datalink level.
The datalink level, also referred to as MTP level 2, resides adjacent and above the physical level and is responsible for providing error detection/correction and properly sequenced delivery of SS7 message packets. Following interpretation/processing at the datalink level, the incoming message is passed up the stack to the network level.
The network level, also referred to as MTP level 3, resides adjacent and above the datalink level and provides the information necessary for message packet routing, message packet discrimination, and message packet distribution. Functionally, message discrimination determines whether the message packet is addressed to the receiving SP or to another SP. If the message contains the local address of the receiving SP, then the message is passed on to message distribution. Message distribution routes the message to the proper application part or user part within the receiving SP. If the message is not addressed to the receiving SP, then it is passed on to the message router, which determines the physical address of the SP to which the message is to be sent. Following interpretation/processing at the network level, the incoming message is passed up the stack to the user parts and application parts level.
The user parts and application parts level resides adjacent and above the network level. User part protocols perform call setup and tear down. Exemplary user part protocols that can be included in SS7 level 4 are ISDN user part (ISUP), telephone user part (TUP), and broadband ISDN user part (BISUP).
Application part protocols provide access to network databases for services, such as 800 number service, credit card verification, and number portability. The transaction capabilities application part (TCAP) protocol is an example of an SS7 level 4 protocol that can be used to provide access to these and other services.
The above description has assumed that an incoming message is being processed. An outgoing message is passed through the protocol stack in the opposite direction, entering at the user part level and exiting from the physical level. FIG. 8 illustrates SS7 protocol architecture relative to SS7 levels and relative to standard Open System Integration (OSI) layers.
The above-mentioned SS7 protocol levels are implemented by hardware and software residing in SS7 signaling points, such as signal transfer points (STPs). A high performance STP is marketed by the assignee of the present application as the Eagle® STP. A block diagram of a conventional Eagle® STP is shown in FIG. 9. A detailed description of the Eagle® STP can be found in the Eagle® Feature Guide PN/9110-1225-01, Rev. B, January 1998, published by Tekelec, the disclosure of which is hereby incorporated herein by reference. As described in this publication, Eagle® STP generally designated 900 includes the following subsystems: maintenance and administration subsystem (MAS) 910, communication subsystem 920 and application subsystem 930. MAS 910 provides maintenance communications, initial program load, peripheral services, alarm processing and system disks. Communication subsystem 920 includes an interprocessor message transport (IMT) bus that is the main communication bus among all subsystems in Eagle® STP 900. This high speed communications system functions as two 125 Mbps counter-rotating serial buses.
Application subsystem 930 includes application cards that are capable of communicating with the other cards through the IMT buses. The illustrated application subsystem 930 includes three types of application cards: link interface module (LIM) 940 that provides SS7 links and X.25 links, application communication module (ACM) 950 that provides a TCP/IP interface for sending copies of SS7 message signal units (MSUs) over ethernet, and application service module (ASM) 960 that provides global title translation, gateway screening and other services. A translation service module (TSM) can also be provided for local number portability.
LIM 940 provides level 1 and some level 2 functions on SS7 signaling links. ACM 950 provides access to a remote host for an STP LAN feature. The STP LAN feature provides unidirectional access to copies of SS7 MSUs from the STP to a remote host. Unidirectional connection from the STP to a host is provided through an ethernet LAN using TCP/IP protocol. Finally, ASM 960 provides additional memory that is used to store translation tables and screening data. A detailed description of the Eagle® STP is provided in the above-cited Feature Guide and need not be further described.
A brief conceptual overview of the Eagle® STP is provided in the brochure entitled Eagle® STP Platform, Publication 908-0126-01, Rev. A, Tekelec, 1997. As described therein, the Eagle® STP is a high capacity, fully fault tolerant packet switch and self-contained local area network for exchanging data messages between a half-dozen to several hundred or more message processing modules. In the Eagle® STP system architecture, three functionally specific application subsystems access each other via a communications subsystem which includes dual counter-rotating, 125 Mbps IMT buses. The application subsystems include LIMs that provide SS7 and X.25 access to telecommunication signaling networks, ACMs that provide TCP/IP access to local area networks and a MAS that provides maintenance communication, peripheral services alarm processing and system disks. As stated in this brochure, “ACMs communicate directly with external, collocated service application systems via a TCP/IP, 10 Mbit/sec LAN interface mounted on the Ethernet Interface Appliqué (EIA). Examples of external application systems include: an SCP not equipped with SS7 signaling links, a routing or charging database system, cellular/PCS home or visitor location registers (HLR, VLR), a message accounting system, a voice/record/image processing system, and other intelligent network (IN) service nodes and peripherals that require direct interface via SS7 signaling links.” Thus, the Eagle® STP platform publication does not describe communication between an STP and an SS7 node. The ACM card described therein is used primarily for diagnostic purposes.
A detailed description of the operation of the Eagle® STP-LAN interface feature is provided in the brochure entitled Eagle® STP STP LAN Interface Feature, Publication 908-0134-01, Rev. B, Tekelec 1997. As described therein, “The STP-LAN Interface Feature enables the collection of copies of SS7 messages that transit the Eagle® STP. This feature, along with user-provided data processing equipment, allows the Eagle® STP to perform functions beyond normal Signal Transfer Point (STP) functionality, such as auditing and accounting functions, message trap and trace and protocol conformance analysis. The Eagle® STP-LAN Interface Feature enables the user to connect external data collection or processing systems directly to the Eagle® STP via TCP/IP, 10 Mbits/sec Ethernet LAN. It enables a user to select either ISUP messages, SCCP/TCAP messages, or both, for transfer to the external monitoring system. It also adds a time-stamp to identify the selected messages and their sequence for subsequent processing.” As is also shown in this brochure, the Ethernet LAN link is a unidirectional link from the ACM to an external processor (host) for diagnostic purposes. Moreover, the Eagle® STP LAN feature is not suitable for communicating SS7 messages between SS7 signaling points, not to mention communicating messages to SS7 signaling points for call setup or other call-related signaling functions.
While communicating SS7 messages over SS7 links can be desirable in some instances, it can also be desirable to communicate SS7 messages over other types of networks. SS7 links provide a high-bandwidth, reliable communication medium for SS7 messages. However, a dedicated SS7 link is expensive and often provides too much bandwidth for a given application. In addition, the proliferation of networks other than SS7 networks makes these networks possible candidates for SS7 message traffic. One type of network conventionally used to transport SS7 messages is an X.25 network. For example, it is known to provide a database transport access feature that intercepts SS7 message signaling units originating from an X.25 network. This feature is described in a brochure entitled Eagle® STP Database Transport Access Feature, Publication 908-0136-01, Rev. B, Tekelec, 1997.
It is also known to use protocol converters for some protocols in connection with STPs. For example, the Eagle® STP X.25 protocol conversion feature provides interfacing and connectivity between nodes on an SS7 network and nodes on an X.25 network. This feature is described in a brochure entitled Eagle® STP X.25 to SS7-IS.41 Protocol Conversion Feature, Publication 908-0135-01, Rev. B, Tekelec, 1997. Similarly, it is known to provide an ANSI-ITU gateway to enable an Eagle® STP to interconnect to other types of signaling networks. This feature is described in a brochure entitled Eagle® STP ANSI-ITU Gateway Feature, Publication 908-0133-01, Rev. B, Tekelec, 1997.
Protocol converters are also known for translating protocols between SS7 and non-SS7 networks. For example, the Tekelec SS7-Frame Relay Access Device (FRAD) translates SS7 protocol information between an SS7 network and a frame relay network. This feature is described in a brochure entitled SS7-Frame Relay Access Device SS7 Protocol Information Translator, Publication 908-0167-01, Rev. A, Tekelec, 1997.
Protocol conversion for SS7 networks is also described in U.S. Pat. No. 5,793,771 to Darland et al., entitled “Communication Gateway” (hereinafter, “the '771 Patent”). The '771 Patent describes a system and method for protocol translation between a foreign postal telephone and telegraph network and a domestic communication service provider, for verifying international credit card numbers. The system includes a communications gateway that consists of a computer located between the foreign network and the domestic network exclusively for performing protocol conversion. The communications gateway is not a signal transfer point. The communications gateway is only a protocol converter, and the communications gateway includes an SS7 module for sending and receiving a plurality of incoming and outgoing SS7 queries and responses. The communications gateway also includes an inbound subsystem module, coupled to the SS7 module, for translating the incoming SS7 queries from an SS7 protocol to a non-SS7 protocol.
The '771 Patent discloses that the inbound subsystem module converts incoming SS7 messages into network information distributed service (NIDS) format and TCP format. However, the only type of SS7 messages that are discussed are TCAP messages, where MTP and SCCP layers are removed from the messages and a TCP header is added to the messages. The translated incoming queries are forwarded to an end user using the non-SS7 protocol. The inbound subsystem module also translates any responses corresponding to the incoming SS7 queries from the non-SS7 protocol to the SS7 protocol.
The communications gateway of the '771 Patent further includes an outbound subsystem module, coupled to the SS7 module, for translating outgoing SS7 queries from the non-SS7 protocol to the SS7 protocol. Again, these queries are disclosed as being TCAP queries for international credit card verification. The translated outgoing queries are sent via the SS7 module across an SS7 network. The outbound subsystem module also translates SS7 responses corresponding to the outgoing SS7 queries from the SS7 protocol to the non-SS7 protocol. The translated responses corresponding to the outgoing SS7 queries are forwarded to an end user while in the non-SS7 protocol.
U.S. Pat. No. 5,706,286 to Reiman et al., entitled “SS7 Gateway” discloses a protocol converter separate from an STP that converts TCAP queries to NIDS format and vice-versa for credit card validation.
U.S. Pat. No. 5,640,446 to Everett et al., entitled “System and Method of Validating Special Service Calls Having Different Signaling Protocols” discloses a protocol converter external to an STP that converts TCAP queries to NIDS format for calling card transactions.
One problem with conventional protocol converters is that these devices require specialized processing hardware and software that reside in a separate location from the STP. These protocol converters also lack the processing speed and functionality of a signal transfer point, such as the above-mentioned Eagle® STP.
Yet another problem with conventional protocol converters is that the protocol converters are incapable of converting SS7 messages to other protocols without terminating the layer being transported. As a result, protocol converters can be required to implement the entire protocol stack.
Yet another problem with the above-mentioned protocol converters is that they only address translation between SS7 TCAP messages and TCP packets. In encapsulating TCAP messages, the MTP layer 3 information is stripped from the message. There are numerous other SS7 message payload types (ISUP, TUP, BISUP, etc.) that cannot be TCP/IP-encapsulated and routed through an IP network without including at least some of the routing label information contained in MTP level 3. The functionality of such SS7 messages is impaired, if not destroyed in many cases without this MTP lower level or routing label information. In practice, such a protocol conversion task presents a more difficult and challenging problem than the relatively simple case of TCP/IP-encapsulated TCAP/SCCP information.
Accordingly, there exists a long-felt need for methods and systems for transmitting SS7 user part messages including lower-level MTP protocol information, over an IP network using signal transfer points.